Mepolizumab and exacerbations of refractory eosinophilic asthma

Abstract

Background: Exacerbations of asthma are associated with substantial morbidity and mortality and with considerable use of health care resources. Preventing exacerbations remains an important goal of therapy. There is evidence that eosinophilic inflammation of the airway is associated with the risk of exacerbations.

Methods: We conducted a randomized, double-blind, placebo-controlled, parallel-group study of 61 subjects who had refractory eosinophilic asthma and a history of recurrent severe exacerbations. Subjects received infusions of either mepolizumab, an anti-interleukin-5 monoclonal antibody (29 subjects), or placebo (32) at monthly intervals for 1 year. The primary outcome measure was the number of severe exacerbations per subject during the 50-week treatment phase. Secondary outcomes included a change in asthma symptoms, scores on the Asthma Quality of Life Questionnaire (AQLQ, in which scores range from 1 to 7, with lower values indicating more severe impairment and a change of 0.5 unit considered to be clinically important), forced expiratory volume in 1 second (FEV(1)) after use of a bronchodilator, airway hyperresponsiveness, and eosinophil counts in the blood and sputum.

Results: Mepolizumab was associated with significantly fewer severe exacerbations than placebo over the course of 50 weeks (2.0 vs. 3.4 mean exacerbations per subject; relative risk, 0.57; 95% confidence interval [CI], 0.32 to 0.92; P=0.02) and with a significant improvement in the score on the AQLQ (mean increase from baseline, 0.55 vs. 0.19; mean difference between groups, 0.35; 95% CI, 0.08 to 0.62; P=0.02). Mepolizumab significantly lowered eosinophil counts in the blood (P<0.001) and sputum (P=0.002). There were no significant differences between the groups with respect to symptoms, FEV(1) after bronchodilator use, or airway hyperresponsiveness. The only serious adverse events reported were hospitalizations for acute severe asthma.

Conclusions: Mepolizumab therapy reduces exacerbations and improves AQLQ scores in patients with refractory eosinophilic asthma. The results of our study suggest that eosinophils have a role as important effector cells in the pathogenesis of severe exacerbations of asthma in this patient population. (Current Controlled Trials number, ISRCTN75169762.)

Figure 1. Numbers of Patients Who Were Screened, Enrolled, and Assigned to a Study Group and Who Completed the Study

All subjects were recruited from a database of patients who were attending our refractory-asthma clinic. Of the 449 persons in the database, 52.3% had a history of sputum eosinophilia of more than 3% on at least one occasion in the previous 2 years, and 63.4% of these patients had been treated with two or more courses of oral corticosteroid therapy in the previous 12 months.

Figure 2. Severe Exacerbations during the Course of the Study

Panel A shows the cumulative number of severe exacerbations that occurred in each study group over the course of 50 weeks. Panel B shows the distribution of the number of exacerbations among subjects in each study group during the treatment period of the study. The mean number of exacerbations per subject over the course of the 50-week treatment period was 2.0 in the mepolizumab group, as compared with 3.4 in the placebo group (relative risk, 0.57; 95% confidence interval, 0.32 to 0.92; P=0.02).

Figure 3. Comparison of Secondary Outcomes between Study Groups

Panel A shows geometric mean (log₁₀ SE) eosinophil counts in blood and sputum specimens, the provocative concentration of methacholine required to cause a 20% fall in FEV₁ (PC₂₀), and mean scores on the Asthma Quality of Life Questionnaire (AQLQ). The AQLQ comprises 32 items, each of which is scored on a scale of 1 to 7, with higher scores indicating better asthma-related quality of life. The items are grouped into four domains, and the reported score is the mean of responses across the four domains. Longitudinal data on PC₂₀ were available for 16 and 18 subjects in the mepolizumab and placebo groups, respectively. Panel B shows mean symptom scores, the forced expiratory volume in 1 second (FEV₁) after bronchodilator use, and the geometric mean (log₁₀ SE) fraction of exhaled nitric oxide at an expiratory flow of 50 ml per second (Fe_NO) before, during, and after the treatment phase of the study. The score on the modified Juniper Asthma Control Questionnaire (JACQ) represents the mean of responses to five questions about daytime and nighttime symptoms and limitation of activities, with each response scored on a scale of 0 to 6; higher scores represent worse symptoms. The mean visual-analogue score represents the total scores divided by 3 for cough, wheezing, and breathlessness, each of which was assessed on a 100-mm scale, with “no symptoms” at one end and “the worst symptoms ever” at the other end. Higher scores indicate worse symptoms. These factors were evaluated before and after administration of 0.5 mg of prednisolone per kilogram per day, with a maximum dose of 40 mg per day, for 14 days, at the beginning and end of the treatment phase. The purple bars represent the 2-week course of prednisolone therapy. P values are for the mean difference between the groups for the change from baseline to the mean or geometric mean of the post-treatment values. Further details are given in Tables 1 and 2 in the Supplementary Appendix. The term ppb denotes parts per billion.